When we say "ascend" we mean to go up, like when you climb up a ladder or go to the top of a slide. It's like getting closer to the sky or the ceiling.
When something or someone ascends, they move upward. This might happen when balloons rise into the air, when airplanes take off, or when you ride an elevator to a higher floor in a building. It's like going from the bottom of a mountain to the top of the mountain.
Sometimes we use the word "ascend" to talk about things that are more abstract or not physical. For example, if someone is promoted at work to a higher position, we might say they are ascending the company's ranks. This means they are moving up in the company and taking on more responsibility. It's kind of like moving up a ladder of success.